The invention relates to a fluid friction coupling having a coupling hub and a coupling housing rotatable on the coupling hub. Outer plates are arranged in the coupling housing and are non-rotatingly connected thereto via teeth, and inner plates are arranged on the coupling hub and are non-rotatingly connected thereto via teeth. The plates of one set of plates being are spaced via spacing means and the plates of the other set of plates are axially movable in the free spaces provided in this way.
With such fluid friction couplings, as known from DE 38 28 421 C, spacing is achieved by so-called spacer rings of a predetermined thickness. These spacer rings are slotted and as compared to the inner diameter of the coupling housing, they have a slightly increased outer diameter so that they rest against the inner housing wall in a prestressed condition. However, a disadvantage of this design is that automatic assembly of the plates is either not possible at all or causes great difficulties, which is the reason why the plates are fitted by hand. Such spacer rings have a further disadvantage in that producing such circular plates from steel wire is relatively complicated and expensive, and they are relatively heavy, as a result of which the weight of the finished fluid friction coupling is increased considerably. Furthermore, such spacer rings require a slightly larger outer diameter than the diameter of the coupling housing in order to ensure that they rest against the inner wall of the coupling housing in a prestressed condition so that they cannot slide into the region of rotation of the inner plates fitted between the outer plates.
From U.S. Pat. No. 3,058,027, it is known to arrange a certain number of teeth on the plates in an angular position in order to achieve a spring-loaded return. However, for spacing the plates, such an angular position is not suitable because the tolerances of the outer diameter and especially centering of the plates have to be very close to achieve uniform dimensions for the distances to be observed, whereas an articulated position, because of its spring-loaded return forces, does not permit such tolerances or only with considerable effort.
From DE 37 26 641 C1, it is known to provide one of the sets of plates with cam-like pressed-out regions which are aligned relative to each other in one direction of rotation and which increase the distance between the associated plates. However, it is the purpose of this design to provide the fluid friction coupling with different torque characteristics for the two directions of rotation. A predetermined distance between the plates cannot be achieved with such pressed-out regions.